Optical fibers are the backbone of modern telecommunications infrastructure. That is the case even for wireless applications, where base stations are connected to the fiber network to support 4G and 5G data rates. Optical fibers are also crucial for optical sensing and RF signal processing systems. The length of optical fiber deployed worldwide is estimated to be approximately equivalent to the distance between the sun and the planet Neptune!

All of this fiber is almost unnoticeable in the background – installed on poles, underground, or in the ocean. But have you ever wondered how optical fiber actually works? What is the structure of optical fiber, and how does light travel through it? If you have no idea, let us help you understand it with an example.

Let’s imagine you have a long, skinny, round rod made of glass or plastic, usually with a protective coating. This rod is called an optical fiber, and it's used to send light from one place to another.

When the light travels through the fiber, it can take different paths or "modes." It's kind of like the different paths you could take walking down a hallway: you could either walk straight down the middle, or you could zigzag from side to side.

The specific path that the light takes can affect how fast it travels and how much it bends as it moves through the fiber. So, when people talk about the "mode" of an optical fiber, they're talking about which path the light is taking inside the fiber.

Technically put, in an optical fiber, a mode is a potential channel for the light. Modes are distinguished by the number of times the light wave circumnavigates the fiber core and the quantity of guided light rays present in the core. The index of refraction and core diameter of the fiber determine how many modes it can support. Choosing the right type of fiber is part of making sure the light gets where it needs to go without losing too much energy along the way.

Types of Optical Fiber Modes:

Primarily, there are two types of optical fiber modes found in an optical fiber cable:
Long-distance transmission uses single-mode fiber, which only allows one path for light to travel through the fiber. Shorter-distance transmission uses multimode fiber, which supports multiple light modes.

Single-mode:

A single-mode optical fiber, also known as fundamental or mono-mode, is a type of optical fiber used in optical fiber communication that is designed to carry only the transverse mode of light. It is the only option for long distance fiber network distribution due to its low signal attenuation, the power loss over distance. Single-mode fiber optic transmissions can travel farther without signal amplification or regeneration than multimode transmissions.

Multimode:

Multimode optical fiber is a type of optical fiber that can transmit multiple optical signals simultaneously in different modes. It is frequently used for cost-effective short-distance communication, generally with higher bandwidth than copper cable. It is generally suitable to cover the majority of enterprise and data center network transmission distance ranges.

Difference between single-mode and multimode optical fibers:

Let’s have a look at the major differences between a single-mode and multimode optical fiber:

Single Mode Vs Multimode Optical Fiber

Comparison between Single Mode and Multimode Optical Fiber

Advantages of using single-mode optical fiber:

Single-mode optical fiber has several advantages over multimode optical fiber, including:

Longer Distances:

As noted above, single-mode optical fibers can transmit signals over much longer distances than multimode fibers.

Higher Bandwidth:

Single-mode fibers have a higher bandwidth than multimode fibers, meaning they can transmit more data at higher speeds. This is because they operate at a higher frequency, allowing for more data to be transmitted through the fiber.

Better Signal Quality:

Because single-mode fibers have a smaller core diameter, they produce less signal distortion than multimode fibers. This means that the signal is clearer and more reliable, making it ideal for long-distance communications.

Security:

Single-mode fibers are more secure than multimode fibers because they are more difficult to tap. This is because they have a smaller core diameter, making it more difficult to access the signal without disrupting it.

Compatibility:

Single-mode fibers are compatible with a wider range of equipment and devices than multimode fibers. This is because they are the standard for many high-speed communication networks, making them widely available and easy to use.


Advantages of using multimode optical fiber:

Multimode optical fibers have several advantages over single-mode optical fibers, including:

Lower System Cost enabled by Larger Core Diameter:

Multimode fibers have a larger core diameter than single-mode fibers, which makes them easier to work with and allows them to transmit more light at lower power levels. This means that they can be used with lower-cost transceivers, which can save money on overall system costs.

Easy to Install:

Because of their larger core diameter, multimode fibers are easier to install and terminate than single-mode fibers. This can save time and labor costs in the installation process.

Wider Selection of Light Sources:

Multimode fibers can be used with a wider selection of light sources, including LEDs and lower-cost laser diodes, which can reduce system costs.

Resilience to Certain Types of Distortion:

Multimode fibers are less susceptible to certain types of distortion, such as modal dispersion, which can affect signal quality in single-mode fibers over long distances.


Making a choice

When it comes to fiber optic systems, the choice between single-mode and multimode fiber is an important one, as it can impact the cost and performance of the system. While multimode fiber has the potential to be more cost-effective in the long run due to its ability to cover distances with a lower bit error rate, it is generally more expensive to produce than single mode fiber. This is because the core of multimode fiber is less precise and has a graded refractive index profile, which means the chemical mix feeding the core deposition process is constantly changing. This makes the process more complicated and results in smaller preforms and more scrap and changeovers per length of good fiber. Additionally, multimode fiber requires a larger amount of germanium, which is an expensive tool used to control refractive index. On the other hand, single mode fiber has a flat refractive index profile and requires less germanium, resulting in a lower overall cost. When deciding between single and multimdode fiber for a fiber optic system, it's important to consider the specific needs of the system in terms of distance, bandwidth, and budget.
There are many optical fiber manufacturers in India, but if you desire the highest quality, HFCL may be the ideal option for you. With cable solutions ranging from 1F to 1728F, HFCL's products can be customized for a multitude of applications, including long-distance transmission, metro networks, mobile networks, access networks, FTTx networks, and more. Our OFCs are created in completely automated and regulated environments at our three advanced manufacturing facilities located in Goa, Chennai, and Hyderabad.

FAQs

When light travels through an optical fiber, it follows a specific path called a mode. When light is transmitted through an optical fiber, it can propagate through the fiber in different paths or modes. The number of modes that can propagate through an optical fiber depends on the fiber's core diameter and the refractive indices of the core and cladding materials.
The number of modes that can propagate through the fiber is determined by the fiber's core diameter and the refractive indices of its core and cladding materials. The mode can impact the transmission characteristics of the signal, including its dispersion and attenuation as it travels through the fiber.

There are two main types of modes in optical fiber:
Single-mode: In single-mode fibers, the core is small enough that only one mode of light can propagate through it. This results in a very focused, direct beam of light that can travel long distances without significant attenuation or distortion. Single-mode fibers are used for high-speed, long-distance applications such as telecommunications, data centers, and internet backbones.
Multimode: In multimode fibers, the core is larger and can support multiple modes of light propagation, resulting in a broader beam of light that can travel shorter distances before experiencing signal degradation. Multimode fibers are typically used for shorter distance applications, such as local area networks, data centers, and video transmission.
There are also different types of multimode fibers, which are classified according to the index of refraction profile of the fiber. These include step-index multimode fibers, graded-index multimode fibers, and dispersion-shifted multimode fibers. Each type of multimode fiber has its own advantages and disadvantages, depending on the specific application requirements.

In a single-mode fiber, there is only one path for the light to travel. Single-mode fibers have a very small core diameter, typically 8 to 10 microns (µm). These fibers are ideal for long-distance applications due to their ability to transmit signals over long distances with little to no signal distortion or attenuation.